Updating the Postfix configuration to use SendGrid as a relay host is easy. For more advanced configuration scenarios, you'll need to refer to the Postfix documentation.
Some implementations of Postfix only allow passwords to contain letters and numbers, meaning you may need to ensure your SendGrid password is only alphanumeric.
Find your Postfix config file, typically /etc/postfix/main.cf, and add the following:
smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd smtp_sasl_security_options = noanonymous smtp_sasl_tls_security_options = noanonymous smtp_tls_security_level = encrypt header_size_limit = 4096000 relayhost = [smtp.sendgrid.net]:587
Now you need to specify your credentials (optionally, use
apikey as username and an API Key as password) in the separate file /etc/postfix/sasl_passwd (you'll likely need to create it):
Next, make sure the file has restricted read and write access only for root, and use the
postmap command to update Postfix's hashtables to use this new file:
$ sudo chmod 600 /etc/postfix/sasl_passwd $ sudo postmap /etc/postfix/sasl_passwd
Finally, restart Postfix:
$ sudo systemctl restart postfix
If you are getting no mechanism available error messages, it generally indicates that you are missing some SASL authentication libraries.
Install the missing module dependency using apt-get (i.e., Debian, Ubuntu):
$ apt-get install libsasl2-modules
Or using a yum (i.e., RedHat, Fedora, CentOS):
$ yum install cyrus-sasl-plain
If port 587 is not working for you, please try 2525 in your postfix config. You may also need to edit /etc/postfix/master.cf to remove # from
tlsmgr unix - - n 1000? 1 tlsmgr.
For other potential errors, please navigate to the default maillog file on your server for debugging purposes. For a CentOS server, the file is in path /var/log/maillog by default.
This file not only reports that the server was unable to use SendGrid to send email but also serves as an excellent debugging tool for new users that catalogues server parameters.